With the rapid development of data processing and information systems, man-machine interface devices are becoming increasingly important. For example, in many applications the efficiency with which an operator can generate and input data to an information processing system is severely limited due to the long-used, conventional keyboards which are the most common form of human operated data input devices.
Conventional data processing keyboards, which have their origins in the alphanumeric key set used in typewriters, have been modified in various ways in order to increase their efficiency and versatility. Such improvements sometimes take the form of additional, special function keys, thus increasing the complexity and size of the keyboard. The rapid miniaturization of data processing systems afforded by microcomputers and very large scale integrated circuits (VLSI's) has vastly increased the applications for microprocessor-based systems; however, the more complex keyboards required to perform complex data input functions for these applications are sometimes unsuitable because of their size and/or complexity.
Others in the past have recognized the need for flexible keyboards which may be employed in various modes to suit different applications. For example, a removable overlay is sometimes placed over the keyboard which has indicia thereon associated with the keys. By employing different overlays, the keyboard can be employed to generate different sets of information.
One limitation of prior alphanumeric keyboards lies in the fact that they are dependent upon the operator's use of an alphabetic-type keyboard to generate information in which each letter of the alphabet has associated therewith a particular key to be actuated. This type of keyboard not only requires a relatively large amount of space which may be impractical to provide in many applications, but is also rather illogical in layout, is not easy to learn for the layperson, and is relatively inefficient in generating information since the keys must be sequentially actuated.
It is therefore a primary object of the present invention to overcome each of the deficiencies inherent in the prior art devices mentioned above.